Neuro-axonal brain viability does not differ between benign and early relapsing-remitting multiple sclerosis patients

Background: The term benign multiple sderosis (BMS) indicates a favorable course of multiple sclerosis (MS), when patients have mild or no disability several years after the clinical onset of the disease. Axonal damage, which is considered a major determinant for the accumulation of disability in MS, can be measured in vivo using proton magnetic resonance spectroscopy (1H-MRS). Objective: To quantify the severity of 'global' axonal damage in BMS and early relapsing-remitting MS (RRMS) patients using whole brain N-acetyl aspartate (WBNAA) 1H-MRS, to better elucidate the structural correlates of a non-disabling disease evolution. Methods: WBNAA concentration was measured in 48 patients with BMS and 17 patients with early RRMS, using an unlocalized ad hoc 1H-MRS sequence. Conventional dual echo and T1-weighted scans were also obtained to measure T2-hyperintense lesion load (T2LL) and normalized brain volume (NBV). Results: T2LL was higher in BMS than in early RRMS patients (p=0.018), while neither NBV nor WBNAA concentration significantly differed between the two groups of patients. No correlations were found between WBNAA concentration and Expanded Disability Status Scale (EDSS), T2LL and NBV. Conclusions: The similarity in the WBNAA concentration between BMS and early RRMS patients fits with the hypothesis that a non-disabling, long-term evolution of MS may be due, at least in part, to the preservation of axonal density and integrity. Such a condition seems to be independent from the burden of MRS-visible lesions.